1. Field of the Invention
The invention relates to a control apparatus and control method of an in-cylinder injection type spark ignition internal combustion engine.
2. Description of the Related Art
By creating a tumble flow inside a cylinder of an in-cylinder injection type spark ignition internal combustion engine and then adequately strengthening that tumble flow with fuel injected near bottom dead center (BDC) on the intake stroke during homogeneous combustion, the tumble flow can be maintained until the ignition timing. This improves the combustion rate of the air-fuel mixture, thus enabling good homogeneous combustion to be achieved. As technology relating to this kind of fuel injection, Japanese Patent Application Publication No. JP-A-2003-322022, for example, proposes a fuel injection control apparatus that strengthens the circulatory airflow within the cylinder using fuel injected from a fuel injection valve. Also, as technology which strengthens the intake airflow within the cylinder during homogeneous combustion, Japanese Patent Application Publication No. JP-A-2005-180247, for example, proposes an intake control apparatus for an in-cylinder direct injection type internal combustion engine that strengthens the intake airflow by controlling an intake airflow control valve provided in an intake passage. Also, Japanese Patent Application Publication No. JP-A-10-159619 proposes technology that improves the homogeneity of the air-fuel mixture by performing a split injection in which some of the fuel is injected during the first half of the intake stroke and the rest of the fuel is injected during the last half of the intake stroke.
However, in the in-cylinder injection type spark ignition internal combustion engine described above, when the air-fuel ratio is lean, the amount of air in the cylinder is greater than it is with the stoichiometric air-fuel ratio so the mass of the tumble flow increases. As a result, even if fuel is injected as described above, the tumble flow is no longer able to be sufficiently strengthened. In this case, the attenuation of the tumble flow makes it no longer possible to ensure that the tumble flow will be sufficiently strong at the ignition timing. Therefore, the swirl of the air-fuel mixture is no longer able to be maintained until the ignition timing. Furthermore, if the swirl of the air-fuel mixture is unable to be sufficiently maintained until the ignition timing, the combustion rate will become too slow which has adverse affects, such as it increases the tendency for knocking to occur, and thus makes good combustion unable to be achieved.
Also, when improving output by the latent heat of vaporization effect in the high load operating range in the foregoing in-cylinder injection type spark ignition internal combustion engine, the injection timing is changed so that it becomes farther from near BDC of the intake stroke and closer to top dead center (TDC) of the intake stroke as the engine speed increases because it is important to inject the fuel during a period when the most air enters the cylinder. On the other hand, in this case the piston position during fuel injection is also approaching TDC so the space within the cylinder during the fuel injection becomes narrower. However, when that space is narrow, the tumble flow does not swirl well so in this state it is difficult to strengthen the tumble flow even if fuel is injected. That is, in this case, although the latent heat of vaporization effect can be obtained, there still remains room for improvement with respect to the homogeneity of the air-fuel mixture and the combustion rate.